1. Field of the Invention
The present invention relates to an optical cable, and more particularly to a high-density optical cable.
2. Description of the Related Art
Currently, the demands for compact, light weight, and high-density optical cables are growing as there is a shortage of installation spaces for the new cables due to the already occupied optical cables. To address this, an attempt to reduce the outer diameter of the optical cables has been made to make possible installation of such cables in the existing narrow ducts.
FIG. 1 is a sectional view illustrating a conventional compact optical cable. The compact optical cable comprises multiple cores of optical fibers 110, a tube 120 surrounding the optical core members, two pairs of core strength members 140, and a sheath 130. The tube 120 has the shape of a hollow cylinder and includes the multiple cores of optical fibers 110 mounted therein. The tube 120 has a thickness of about 1 mm. The sheath 130 with a predetermined thickness is formed by an extrusion process and surrounds the tube 120. The sheath constitutes the outermost layer of the compact optical cable to protect its interior components against the external environment.
The two pairs of the core strength members 140 complement the mechanical weakness of the optical cables to a certain extent. However, if the external stress is severe, the strength members tend to deteriorate the mechanical properties of the optical cables.
FIGS. 2 and 3 are illustrates the shape of the compact optical cables shown in FIG. 1 when an excessive stress is applied. As shown in FIG. 2, the external stress 150 is applied to the outer sheath layer of the cable, then, as shown in FIG. 3, the optical cable gets severely deformed by the stress applied thereto. The strength members 140, which have been originally arranged inside the sheath 130, penetrate into inside the sheath and press the tube 120 when subject to stress. Note that the tube 120 has a thickness of about 1 mm, but the strength members 140 have a higher degree of hardness than those of the tube 120 or sheath 130. As result, the optical fibers 110 mounted inside the tube 120 are subject to severe stress due to the movement of the strength members 140.
As described above, the conventional compact optical cable is provided with a plurality of strength members to increase the mechanical strength of the cable. However, the strength members tend to have opposite effect if excessive external stress is applied to the cable.